docs: def streamDefByThreshold(self,
                               stream_raster_grid,
                               threshold,
                               contributing_area_grid,
                               mask_grid=None,
                               ):
          """
          Calculates the stream definition by threshold.
          """
          log("PROCESS: StreamDefByThreshold")
          self.stream_raster_grid = stream_raster_grid
  
          # Construct the taudem command line.
          cmd = [os.path.join(self.taudem_exe_path, 'threshold'),
                 '-ssa', contributing_area_grid,
                 '-src', self.stream_raster_grid,
                 '-thresh', str(threshold),
                 ]
  
          if mask_grid:
              cmd += ['-mask', mask_grid]
  
          self._run_mpi_cmd(cmd)
  
          # create projection file
          self._add_prj_file(contributing_area_grid,
                             self.stream_raster_grid)